1. Field of the Invention
The present invention relates to a picture signal processing unit that performs frame rate conversion of a picture signal by using motion compensation, to a picture signal processing method, and to an image display unit including the picture signal processing unit.
2. Description of the Related Art
As one of picture signal processing for improving image quality in a television receiver, a DVD (Digital Versatile Disk) player and the like, there is frame rate conversion which utilizes motion compensation.
A description will be given of the principles of the frame rate conversion by taking a picture signal obtained by a television broadcasting camera (hereinafter referred to as a camera signal) as an example with reference to FIG. 11A to FIG. 13C.
FIG. 11A illustrates original frames A, B, C, and D of an NTSC (National Television System Committee) type camera signal. FIG. 11B illustrates a case in which the frame rate of the camera signal is converted from 60 Hz (normal rate) to 120 Hz (double rate). That is, every one interpolation frame is added to between adjacent original frames (between the frame A and the frame B, between the frame B and the frame C, and between the frame C and the frame D) at intervals of 1/120 sec.
FIGS. 12A and 12B illustrate a case in which the frame rate of the camera signal is converted from 60 Hz (normal rate) to 240 Hz (quadruple rate). That is, every three interpolation frames are added to between adjacent original frames (between the frame A and the frame B, between the frame B and the frame C, and between the frame C and the frame D) at intervals of 1/240 sec.
Each interpolation frame is generated by interpolating a picture of a previous original frame and a picture of a subsequent frame. Such interpolation is performed based on a parameter of an interpolation position of each picture in each interpolation frame and a motion vector between the previous original frame and the subsequent original frame. Specifically, such interpolation is performed by the following method. That is, after addresses of pixels of the previous and subsequent original frames used for calculating a pixel value of the interpolation frame are calculated based thereon, the pixel values of these addresses are applied with weighting in accordance with the interpolation position.
For example, as illustrated in FIG. 13A to FIG. 13C, such frame rate conversion has an effect of resolving motion blurring in the camera signal and an effect of reducing judder in a motion picture by a film signal. Specifically, first, in the existing picture (60 frames per 1 second: normal rate) illustrated in FIG. 13A, a difference between a first picture A and a next picture B is large and thus a persistence of vision appears. On the other hand, in the double rate picture (120 frames per 1 second) illustrated in FIG. 13B, one interpolation picture A2 is inserted between the picture A and the picture B (middle position: interpolation position=“0.5”), the picture amount is doubled, and thus persistence of vision is more decreased compared to the normal rate picture. Further, in the quadruple rate picture (240 frames per 1 second) illustrated in FIG. 13C, three interpolation pictures A1 to A3 are inserted between the picture A and the picture B (interpolation positions=“0.25,” “0.5,” and “0.75”), and thus the picture amount is quadrupled. Thereby, the persistence of vision is further decreased compared to the double rate picture, and the persistence of vision hardly appears.
Examples of technologies for the foregoing frame rate conversion include a technology proposed in Japanese Unexamined Patent Application Publication No. 2003-189257.